After the 33-year-old star announced he was retiring from Ivory Coast duty after a 14-year international career, City coach Pep Guardiola insisted Toure would not feature in his team unless the player apologized for remarks made by his agent, Dimitri Seluk.

Guardiola left Toure out of the club's UEFA Champions League squad -- a move which infuriated Seluk and led to a fierce polemic aimed at the Spaniard.

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Photos:Europe's biggest summer signings

Photos:Europe's biggest summer signings

Premier League spending during the European summer transfer window reached £1.165 billion ($1.544 billion) on deadline day, August 31. Brazilian defender David Luiz rejoined Chelsea from Paris St. Germain for a reported fee of £34 million ($44.7 million).

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Photos:Europe's biggest summer signings

Luiz wasn't the only defender Chelsea signed on deadline day, after paying a reported £23 million ($30.5 million) to bring Marcos Alonso to Stamford Bridge from Italian club Fiorentina. It was the sixth consecutive year spending in England's top division has increased, breaking the £1 billion mark for the first time.

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Photos:Europe's biggest summer signings

Going the other way was Chelsea's Colombia star Juan Cuadrado, who re-signed for Serie A champion Juventus on a three-year loan deal.

After failing to challenge for the Premier League title last season, Arsene Wenger was under pressure to further strengthen his squad with high-profile players -- but it took until August 30 for Arsenal to announce the signing of Lucas Perez from Deportivo la Coruna for a reported fee of £17 million ($22 million). The 27-year-old is uncapped by Spain, but scored 17 goals in La Liga last season.

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Photos:Europe's biggest summer signings

Soon after the Perez deal, Arsenal also confirmed the signing of Germany defender Shkodran Mustafi (pictured right at Euro 2016) from Valencia. The fee was undisclosed but British media reported it to be above £30 million ($39 million).

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Midfielder Jack Wilshere left Arsenal to join Bournemouth on a season-long loan, after manager Arsene Wenger couldn't guarantee the England international regular first team football.

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Barcelona goalkeeper Claudio Bravo signed for Manchester City on August 25, joining former manager Pep Guardiola for a reported fee of £15.3 million ($20 million).

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He replaced Joe Hart, who was deemed surplus to requirements by Pep Guardiola and promptly loaned out to Italian club Torino on August 31.

On June 30, Brazil forward Hulk became the Chinese Super League's most expensive signing, after joining Shanghai SIPG from Russian club Zenit St. Petersburg for €55.8 million ($60.8 million).

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On June 28, Sadio Mane became the most expensive African player when the Senegal forward joined Liverpool from Southampton in a deal worth a reported £34 million ($44.7 million).

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It might have been a free transfer, but Zlatan Ibrahimovic's July 1 move to Manchester United is one of the biggest deals of the summer window. The free-scoring Swede joined Jose Mourinho after his contract at Paris Saint-Germain expired.

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On July 6, Mourinho made Henrikh Mkhitaryan his second signing at the club, with Manchester United paying Borussia Dortmund a reported fee of $40 million for the Armenia midfielder.

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Photos:Europe's biggest summer signings

Mourinho's first acquisition was Ivory Coast defender Eric Bailly. On June 8, Manchester United announced the 22-year-old's signing from Spanish team Villarreal for a reported £30 million ($39.2 million) fee.

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John Stones didn't play a single minute in England's ill-fated Euro 2016 campaign, but on August 9 the 22-year-old joined Manchester City from Everton for a reported fee of $62.7 million -- which made him the world's second-most expensive defender.

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A week earlier, Leroy Sane had become Pep Guardiola's fifth Manchester City signing, joining from Schalke for a reported fee of $49 million. The 20-year-old made one appearance at Euro 2016, as a substitute in Germany's semifinal defeat by France.

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On July 1, Spain forward Nolito became Guardiola's second signing when Manchester City triggered the €18 million ($20 million) release clause in his Celta Vigo contract.

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On June 2, Germany midfielder llkay Gundogan became Guardiola's first City signing, joining for a reported £20 million ($26 million) fee from Borussia Dortmund.

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Photos:Europe's biggest summer signings

On July 21, Andre Gomes joined Barcelona from Valencia for an initial fee of €35 million ($39 million) after a successful Euro 2016 in which the midfielder helped Portugal win its first international title.

France defender Samuel Umtiti moved to the Spanish champion on July 30, signing a five-year deal after Barca paid French side Lyon €25 million ($27.9 million).

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Barcelona also completed the €16.5 million ($18.4 million) signing of France international left-back Lucas Digne from Paris Saint-Germain on July 13.

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Italy striker Graziano Pelle reportedly became the joint-sixth highest paid player in the world after he left English club Southampton to join Chinese Super League side Shandong Luneng in a £13 million ($17 million) deal on July 11. The 31-year-old will reportedly earn that much in one season.

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On July 30, Spanish club Atletico Madrid signed French forward Kevin Gameiro from La Liga rival Sevilla for a reported €32 million ($35.6 million).

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On June 16, Champions League finalist Atletico also agreed a €25 million ($27.8 million) deal for Benfica's Argentinian midfielder Nicolas Gaitan.

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World Cup winner Mario Goetze rejoined Borussia Dortmund on July 21 after an unsuccessful spell with Bayern Munich, which had made him Germany's most expensive player at the time when it paid €37 million for him in 2013.

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The next day, Dortmund continued to bolster its squad by signing Andre Schurrle from Bundesliga rival Wolfsburg for a reported fee of $33 million.

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On July 16, France midfielder N'Golo Kante was the first star name to be sold from Leicester City's Premier League-winning side, signing for English rival Chelsea in a $42 million deal.

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On July 3, former Juventus and Italy coach Antonio Conte started his Chelsea revolution by signing 22-year-old Belgium striker Michy Batshuayi from French club Marseille for a reported €40 million ($44.5 million).

On July 15, Juventus completed the signing of Morocco defender Medhi Benatia from Bayern Munich on a season-long loan costing €3 million ($3.45 million), with an option to buy for an extra €17 million ($19 million).

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Juventus signed Brazilian defender Dani Alves on a free transfer from Barcelona on June 27 after his contract at the Spanish club expired.

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On June 21, Real Madrid activated the €30 million ($34 million) buy-back clause for Spain striker Alvaro Morata -- who it had sold to Juventus for €20 million ($22.3 million) in 2014.

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Granit Xhaka made headlines at Euro 2016 when his shirt ripped -- before the tournament the Switzerland midfielder had already secured a move to English club Arsenal from Borussia Monchengladbach in a deal worth a reported £30 million ($39.2 million).

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Bayern Munich started the big-money moves in May, when the German champion announced a €35 million deal for Benfica's teenage midfielder Renato Sanches, who would help Portugal win Euro 2016.

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At the same time, Bayern also revealed it had agreed a deal to buy Germany's World Cup-winning defender Mats Hummels for reportedly a similar initial fee from Bundesliga rival Borussia Dortmund.

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Guardiola, who was Barcelona boss when Toure was sold to City in 2010, added that the player, who returned to training on Monday after suffering with a migraine, had not had the "courage" to call him about Seluk's comments.

The midfielder has made just one appearance this season and has yet to feature in the Premier League.

Toure, who has won two English titles with the club, is expected to leave the club in June when his contract expires, though his future will also be under scrutiny during the January transfer window.

"Writing this note was probably 'the most difficult match of my life.' After 14 years at the highest level, I'm sure this is the right time for me.

"The fact that I am 33 now, the intensity of training and the multitude of games are not the reasons why I am making this decision.

"I would like to say solemnly that I am stopping. It's true that I had several titles at clubs, national cups, league trophies. With the Elephants, it was even more special. I learned to win for my country. That's why I will always retain the pride in having achieved four African Golden Balls for the Ivory Coast."